The present invention relates to a hand circular saw with a mitre adjusting device for adjusting mitre angles.
A hand circular saw with adjustable cutting depth is disclosed for example in U.S. Pat. No. 4,856,394. The cutting depth is determined here by the dimension, by which the saw blade projects under the base plate. It can be changed by turning the hand circular saw relative to the base plate around an axis extending parallel to the rotary axis of the saw blade and arrested in a desired position by clamping screws relative to the clamping block arranged on the base plate. For providing comfortable adjustment of the preferred cutting depth, abutments are arranged on the clamping blocks and define the corresponding preferred positions of the saw blade, so that the hand circular saw is supported on the abutments during the selection of the preferred cutting depth. The arrangement for the cutting depth adjustment is relatively bending-resistant and deformation-safe, since the axis for the cutting depth adjustment is short and determined by two bearing blocks arranged at a small distance of approximately 40 mm from one another. There is only a little danger that the saw blade during turning up and down for changing the cutting depth can be unintentionally moved from its position in a plane normal to the base plate. Then a change of the cutting depth adjustment results in alignment deviations of the saw blade from its nominal position.
The situation is however different during adjustment of the saw for a mitre cut. For this purpose the saw is turned about a turning axis parallel to the saw blade and the base plate. The turning axis is relatively long and the bearing blocks which support the turning axis are arranged at a relatively great distance from one another of at least 200 mm. Moreover, the gripping point for the hand of the operator during the inclination adjustment of the hand circular saw is remote from the bearing block or blocks. Thereby a long arm is produced and therefore due to the adjustment forces during the inclined adjustment, high rotary and bending moments are generated on the hand circular saw. This can lead to twisting or canting of parts which are generally composed of thin metal sheets, so that the hand circular saw is turned in a bearing block by 45.degree. and in the opposite bearing block by 43.degree.. Due to the thusly obtained play in the system for adjusting the mitre angle, the starting oblique positions of the saw blade relative to the base plate or to a predetermined cutting plane can occur. Such oblique positions will lead to oblique cutting edges and thereby to faulty saw cuts courses. The above described danger is characteristic especially for hand circular saws with coulisse guides for mitre angle adjustment, which have the advantage of not using a stable, solid turning axis so that the actual turning axis extends under the base plate or on the workpiece.